function popUp(url,width,height){ 
var popUp = window.open(url, 'popupwin', 'width=' + width + ',height=' + height); 
var halfAvailWidth = Math.round(screen.availWidth / 2); 
var halfAvailHeight = Math.round(screen.availHeight / 2); 
var x = halfAvailWidth - (width / 2); 
var y = halfAvailHeight - (height / 2);

popUp.focus();

if(navigator.appName == "Netscape"){ 
popUp.screenX = x; popUp.screenY = y; } 
else { popUp.moveTo(x,y); 
} 
}